Even with the presence of a high-efficiency deaeration system dissolved oxygen sometimes does slip through and enter boiler drums. Mechanical deaeration also at times does face operational problems leading to excessive leakage of dissolved oxygen into the boiler system.
Oxygen corrosion will take place even with an oxygen level of as low as 10 ppb and the results of the corrosion will be significant pitting at the waterline and to a certain extent pitting on tube surfaces.
The use of hydrazine as a chemical oxygen scavenger has been known to provide an excellent result at a very good cost factor but the classification of the product as a suspect carcinogen has made it replaced in many established organizations. Chemco is proposing Catalyzed Sodium Sulfite based oxygen scavenger. It is a volatile metal passivator and more reactive than any other product, even at lower temperatures.